Conventionally, in in-situ solution-mining processes, the leaching solution is brought into contact with the subterranean deposit through a suitable injection system. The leaching solution or lixiviant may be an alkaline or acidic medium which solubilizes the mineral values as it traverses the ore body. Conventionally, the mineral values in an ore body are subjected to an oxidation step in order to convert the mineral values to a soluble form. For example, the tetravalent uranium must be oxidized to its soluble hexavalent form for leaching. The pregnant lixiviant is then withdrawn from the ore body through a suitable production system and treated to recover mineral values therefrom by suitable techniques such as solvent extraction, direct precipitation or by absorption and elution employing an ion exchange resin. The above method and modifications thereof work most efficiently when a fairly uniform formation is the subject of the leaching process. All too often, however, and in fact in the majority of cases, the formations are not uniform as to both porosity and permeability. In some zones, the strata are sufficiently heterogeneous as to severely alter flow patterns of the leaching fluids. Leaching fluids follow the higher permeability streaks thus by-passing portions of the ore body which results in loss of recoverable mineral values due to the lack of contact by leaching fluids. For example, in many uranium reservoirs, 30 to 50 wt.% or more of uranium values may not be recoverable via in-situ leaching because of channelling of leachate through the high permeability zones.
In secondary and tertiary oil recovery processes, the problem of channelling and fingering has also been recognized. Various methods utilizing polymeric material as viscosity builders or solution thickneners have been used as indicated by U.S. Pat. No. 3,434,542 to Dotson et al, U.S. Pat. No. 3,888,308 to Gale et al, U.S. Pat. No. 4,129,182 to Dabbous, U.S. Pat. No. 3,530,938 to Cooper, U.S. Pat. No. 4,066,126 To Waite el al, U.S. Pat. Nos. 3,292,698 and 4,042,030 to Savins et al, and U.S. Pat. No. 4,018,281 to Chang. The polymeric thickener or viscosity builder is normally utilized in either a water bank or a surfactant bank injected into the formation to drive the oil to a production system.
However, such polymeric material as utilized in secondary and tertiary oil recovery degrades and loses it's viscosity building effects when subjected to oxidants. As stated above, oxidants are essential to the in-situ recovery of mineral values such as uranium.
Accordingly, the present invention provides a new method wherein mobility control methods, utilizing polymeric material as thickeners or viscosity builders, are applied to the in-situ recovery of mineral values even when an oxidation step is necessary.